Duplex stainless steel excellent in corrosion resistance

A highly corrosion-resistant duplex stainless steel having a chemical composition:

• 0.05 to 2.0% Si, 0.1 to 4.0% Mn, 1.0 to 4.0% Ni, 20.0 to 26.0% Cr, over 1.0 to 3.0% Cu, 0.002 to 0.05% Al, 0.10 to 0.40% N, 0.05 to 0.50% the sum of at least one of V, Ti and Nb, 0.50% or less Mo, 0.50% or less W, and the balance of Fe and unavoidable impurities, impurity contents being 0.05% or less C, 0.03% or less P and 0.005% or less S;
• wherein the duplex stainless steel has Ni.sub.bal value expressed by the following Equation (1) in the range of -11.0 to -8.0:
• Ni.sub.bal =Ni.sub.eq -1.1.times.Cr.sub.eq +8.2 (1)
• where
• Ni.sub.eq =Ni(%)+0.5.times.Cu(%)+30.times.{C(%)+N(%)} (2)
• Cr.sub.eq =Cr(%)+1.5.times.Si(%)+Mo(%)+W(%) (3).

A highly corrosion-resistant duplex stainless steel having a chemical composition:

• 0.05 to 2.0% Si, 0.1 to 4.0% Mn, 1.0 to 4.0% Ni, 20.0 to 26.0% Cr, over 1.0 to 3.0% Cu, 0.002 to 0.05% Al, 0.10 to 0.40% N, 0.05 to 0.50% the sum of at least one of V, Ti and Nb, 0.0030% or less B, 0.0030% or less Ca, and the balance of Fe and unavoidable impurities, impurity contents being 0.05% or less C, 0.03% or less P and 0.005% or less S;
• wherein the duplex stainless steel has Ni.sub.bal value expressed by the following Equation (1) in the range of -11.0 to -8.0:
• Ni.sub.bal =Ni.sub.eq -1.1.times.Cr.sub.eq +8.2 (1)
• where
• Ni.sub.eq =Ni(%)+0.5.times.Cu(%)+30.times.{C(%)+N(%)} (2)
• Cr.sub.eq =Cr(%)+1.5.times.Si(%)+Mo(%)+W(%) (3).

A highly corrosion-resistant duplex stainless steel having a chemical composition:

• 0.05 to 2.0% Si, 0.1 to 4.0% Mn, 1.0 to 4.0% Ni, 20.0 to 26.0% Cr, over 1.0 to 3.0% Cu, 0.002 to 0.05% Al, 0.10 to 0.40% N, 0.05 to 0.50% the sum of at least one of V, Ti and Nb, 0.50% or less Mo, 0.50% or less W, 0.0030% or less B, 0.0030% or less Ca, and the balance of Fe and unavoidable impurities, impurity contents being 0.05% or less C, 0.03% or less P and 0.005% or less S;
• wherein the duplex stainless steel has Ni.sub.bal value expressed by the following Equation (1) in the range of -11.0 to -8.0:
• Ni.sub.bal =Ni.sub.eq -1.1.times.Cr.sub.eq +8.2 (1)
• where
• Ni.sub.eq =Ni(%)+0.5.times.Cu(%)+30.times.{C(%)+N(%)} (2)
• Cr.sub.eq =Cr(%)+1.5.times.Si(%)+Mo(%)+W(%) (3).
• 5.